Lateral velocity resolution from three-dimensional seismic refraction data | OUP Journals & Magazine | IEEE Xplore

Lateral velocity resolution from three-dimensional seismic refraction data


Abstract:

A method for estimating the lateral velocity resolution from 3-D seismic refraction traveltimes is presented. The method is non-linear in that synthetic data calculated f...Show More

Abstract:

A method for estimating the lateral velocity resolution from 3-D seismic refraction traveltimes is presented. The method is non-linear in that synthetic data calculated from ‘checkerboard’ models are inverted using an iterative tomographic approach incorporating smoothness constraints and updated ray paths at each iteration. Two applications are presented: (1) real data from the Faeroe Basin experiment using the ray coverage and noise level of approximately 50000 picks, and (2) ideal data from the same experiment corresponding to 100 per cent data recovery, equivalent to about three times as many ray paths. The refraction data constrain the sedimentary and basement structure to approximately 12 km depth. A comparison of the results from the two data sets provides a qualitative check on the resolution method, illustrates the pitfalls of using ray coverage as an indicator of resolution, and demonstrates the potential resolution of currently feasible 3-D refraction experiments. 32 checkerboard models consisting of alternating positive and negative velocity anomalies superimposed on the preferred final model of the basin were tested, each with a different cell size, position or orientation. The problem of ray bending associated with the 5 per cent checkerboard anomalies is shown to be small. Using models with four cell sizes allowed for resolution estimates from 3 to 15 km, this range being imposed by the frequency content of the data and the areal dimensions of the study area (44×26 km). An operator centred on each model node measures the local semblance between the known and recovered checkerboard models. A determination of the smallest well-resolved cell size at each model node is then made using a 0.7 semblance threshold to provide a spatially dependent lateral resolution estimate. Resolution for the real data set varies from an average of just over 3 km at 2 km depth, to 10 km at 10 km depth, where there is a local maximum in ray coverage due to a concentration of ...
Published in: Geophysical Journal International ( Volume: 135, Issue: 3, December 1998)
Page(s): 1101 - 1112
Date of Publication: December 1998

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